26 October 2010

Vogt G. 2010. Suitability of the clonal marbled crayfish for biogerontological research: A review and perspective, with remarks on some further crustaceans. Biogerontology11(6): 643–669. http://dx.doi.org/10.1007/s10522-010-9291-6

Abstract

This article examines the suitability of the parthenogenetic marbled crayfish for research on ageing and longevity. The marbled crayfish is an emerging laboratory model for development, epigenetics and toxicology that produces up to 400 genetically identical siblings per batch. It is easily cultured, has an adult size of 4-9 cm, a generation time of 6-7 months and a life span of 2-3 years. Experimental data and biological peculiarities like isogenicity, direct development, indeterminate growth, high regeneration capacity and negligible senescence suggest that the marbled crayfish is particularly suitable to investigate the dependency of ageing and longevity from non-genetic factors such as stochastic developmental variation, allocation of metabolic resources, damage and repair, caloric restriction and social stress. It is also well applicable to examine alterations of the epigenetic code with increasing age and to identify mechanisms that keep stem cells active until old age. As a representative of the sparsely investigated crustaceans and of animals with indeterminate growth and extended brood care the marbled crayfish may even contribute to evolutionary theories of ageing and longevity. Some relatives are recommended as substitutes for investigation of topics, for which the marbled crayfish is less suitable like genetics of ageing and achievement of life spans of decades under conditions of low food and low temperature. Research on ageing in the marbled crayfish and its relatives is of practical relevance for crustacean fisheries and aquaculture and may offer starting points for the development of novel anti-ageing interventions in humans.

19 October 2010

13 October 2010

In August, this story appeared on a German news site about crayfish escaping en masse from a pond near a school in Klepzig, Germany. On 12 October, a follow-up appeared, saying that the crayfish were Marmorkrebs.

This is bad news, if I am reading these new stories right. (I don’t read German, so I am working from a Google translation of the news story. Translation by a person would be welcomed!)

It appears that crayfish were found, in large numbers, walking out of this pond. The reasons were unknown, but overcrowding was given as a possible explanation, seen by the new story as likely given the rapid reproduction of Marmorkrebs.

Martin et al. (in press) pointed out that until now, only single Marmorkrebs have been found in Europe, never a reproducing population. This gave a glimmer of hope that Marmorkrebs might not be able to establish themselves as an invasive species in Europe. That hope glimmers a lot less brightly if the animals are walking out of water because of overcrowding, since that indicates an actively reproducing and expanding population.

Worse, both stories report astonishing sizes of the animals. The first report puts some individuals found in Klepzig at 20 cm long; the later, at 15 cm. If so, those are record-shattering sizes for Marmorkrebs. Vogt (in press) reported:

The largest specimen of my laboratory colony had reached a length of 8.8 cm... Under tropical outdoor conditions the maximum length measured was 10.7 cm (Jones et al. 2009)

50-100% larger than the largest size recorded previously is worth investigating. It suggests that the Klepzig population has been there a long time (since animals don’t grow to that size in a few weeks), and that the conditions are highly conducive to the animals.

The new article emphasizes the potential for Marmorkrebs to carry crayfish plague, which is an entirely legitimate concern. To the best of my knowledge, however, Marmorkrebs have not yet been shown to carry the pathogen. Someone needs to try infecting Marmorkrebs to see how they fare against the disease, and how contagious they are compared to other North American species.

Vogt G. Suitability of the clonal marbled crayfish for biogerontological research: A review and perspective, with remarks on some further crustaceans. Biogerontology: In press.http://dx.doi.org/10.1007/s10522-010-9291-6

12 October 2010

The new paper by Martin and colleagues is a significant one for the Marmorkrebs research community, because it seems to settle the problem of the species most closely related to Marmorkrebs pretty definitively. Marmorkrebs are most closely related to slough crayfish, Procambarus fallax. The picture at right compares the two; P. fallax is on top (Fig. 1 from Martin et al.)

It’s also noteworthy for being the first to tackle the thorny issue of a species name for Marmorkrebs. Martin and colleagues suggest Marmorkrebs be treated as a “form” of P. fallax, and suggest referring to Marmorkrebs as P. fallax f. virginalis. They leave open the possibility that Marmorkrebs might warrant having its own name. If that were to happen, they suggest it become Procambarus virginalis.

It’s pretty easy to guess that the word “virginalis” is derived from the same root as the word “virgin.” This is clearly a nod to Marmorkrebs’ parthenogenetic reproduction.

Now, if I’d written the paper, I’d have suggested the scientific name be “marmoratus,” which is Latin for “marbled.” It ties into the common names for them, marbled crayfish and Marmorkrebs. And it wouldn’t risk anyone thinking that these were white crayfish.

Because “forms” are not recognized by the international committee that oversees scientific names for animals, it’s an open question at this point as to whether this naming scheme will be adapted by the community. I think continuing to use “Marmorkrebs” in addition to the name suggested by Martin and colleagues (or some variant of it) will continue to serve the research community well, for reasons I discussed here. Not only is “Marmorkrebs” distinctive, it can now provide some important continuity in the scientific literature and in search engines.

Additional: Co-author Gerhard Scholtz emailed me with this comment:

(“virginalis”) literally means “related to a virgin.” The Latin words for white are different. Only later in Christian symbolism is the white lilly a sign for the immaculate Mary (immaculate conception) and in addition for giving birth as a virgin. Immaculate conception means that Mary was born without the “original sin” (inherited from from Adam and Eve) not that she gave virgin birth, this is often confused. So the use of “virginalis” for white is very indirect. If we would have chosen “marmoratus”, and we considered this, then the characteristic
difference to P. fallax, which is also marbled, would have been given
away.

And I fully understand the reluctance to use “marmoratus,” which is the same reason I advocate “Marmorkrebs” over “marbled crayfish.” There are an awful lot of crayfish with some sort of marbled colouration.

05 October 2010

There are parthenogenetic vertebrates (some of which have been featured on this blog), but the Mangrove killifish, Kryptolebias marmoratus, is the only vertebrate that regularly self-fertilizes. Most individuals have male and female reproductive organs. Obviously, this allows you to have individuals that are not quite clones, but certainly have much more limited variation than most sexual species.

But, because sex is rarely simple, some individuals in this species are just male.

And that little detail means that the hope that all these individuals will create nice, neat, clone lineages gets shot down. So Tatarenkov and colleagues decided to investigate how genetically similar these fish are to each other.

Some findings are depressingly familiar. Cell biologists have often found that what they thought was one type of cell cultures has been contaminated by nearby strains of other immortal cells. HeLa cells are particularly notorious in this regard. Similarly, Tatarenkov and company found about 20% of their marbled killifish did not have the expected genes. Incomplete record keeping meant that many sources of error, or sources of new variation they found, could not be traced back to its source.

They did find new genetic variation that appeared to have cropped up since the animals had been collected for the lab, which they attributed to new mutations. In fact, one gene seemed to be a mutational “hotspot,” mutating several times in different lines.

The major source of genetic variation, however, was the original source of the lab population. This fish has a wide distribution, and stocks collected from different locations did not resemble each other. Thus, this fish has a nice combination of being able to maintain genetic similarity within a lineage, but there remains some variation across lineages.

P.S. – If this fish’s specific name, “marmoratus,” looks a bit familiar, it’s because it is Latin for “marbled.” And that’s undoubtedly the same root for the word, “Marmorkrebs.”